Note: Descriptions are shown in the official language in which they were submitted.
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`. ATTORNEY DOC~ET NO: 03014/050001
IMPROVED CURRENT LIMITING FUSE
Back~round of the Xnvention
The invention relates to current limiting ~u~es.
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;~ Current limiting fuses typically have one or more
~ ~usible e~ements connecting two conduating terminal~
`~, 5 within an insulative housing.
One type of fu~e construction employs a housing
:; made o~ a tubular casing of melamine glass, cardboard, or
thermoset polymer resins in a matrix with glass or
papers. The ends of the tubes are typically closed with
end caps, which go around the ends of the tube, or end
blocks of brass or copper, which are inside of the tube
at the ends. When end blocks are employed, khere often
are terminal blades that are located on the outer
surfaces of the end blocks ~being either integral with or
attached such as by welding or brazing to the en~
blocks), and fusible elements are connected, e.g., by
welding in grooves, to the inside surfaces of the end
blocks.
Barricklow U.S. Pat. No. 973,250 describes a
different type of ~use construction in which the
insulative housing is made of two pieces that have been
bolted together.
Summary o~ the Inyention
~; In one aspect, the invention features, in general,
making an insulative fuse housing by ultrasonically
',~ welding to~ether housing pieces made of thermoplastic
material. The thermoplastic material has a continuous
use temperature greater than 110 C (most preferably
greater than 120 C) to provide structural integrity at
~ 30 elevated temperatures to which fuses are subjected in
,~ use. The material includes filler (e.g~, fiber glass) in
ri~l a range between 20% and 40% (most preferably between 30
~,l and 35%) to have enough filler to provide a significant
increase of the continuous usie temperature of the
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thermoplastic material but to not have so much filler as
to prevent bonding by ultrasonic welding. Suitable
~i! thermoplastic materials include highly crystalline Nylon
4-61 polyphthalamide, polyphenylene sulfide, and liquid
~*'l 5 crystal polymer.
In another aspec~, ~he invention ~eaturest in
general, a fuse including a ~use housing made ~rom two or
more housing pieces made ~rom molded thermoplastic
material. The housing has end walls with openings
}~l 10 through which terminals pass. The housing also has inner
walls that are integral with and spaced from respective
l end walls and have surfaces that define passages that are
~ aligned ~ith the openings. The terminals are supported
i~,! by the end walls around the openings and by the sur~aces
~:l 15 of the inner walls defining the passages. This
~-7 1 arrangement provides good support for the terminals
without relying on a concentrated mass of thermoplastic
material adjacent to the end walls.
In preferred embodiments, there are two, generally
coplanar, inner walls associated with each end wall; one
~¦ inner wall i8 on one housing piece; the other inner wall
is on another housing piece; there is a epace between the
inner wallsl and the inner walls each have a recess that
~, receives a portion o~ the terminal. The inner walls are
~, , 25 thinner than the end walls, and transverse ribs join each
inner wall with its respective end wall on both æides of
l the terminal. The housing pieces are joined to each
;1l other at a shear joint formed between mating seam
i¦ portions having a stepped con~iguration. The housing
''~ 30 pieces have inter~ering portions at the mating seam
~ portions and are joined together by ultrasonic welding.
!~ In another aspect, the invention features, in
~l general, a fuse which includes an insulative housing that
i has a tubular portion and two end portions that are
.!''~'~ 35 located at the ends o~ the tubular portion and have slots
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$~ through which terminals pass. The housing is made from
?l two plastic housing pieces that have been joined
;~, together. The terminals have portions inside and outside
of the housing, and a fusible element located inside the
housing has ends connected to each o~ the terminals.
This approach permits reducing the number of parts and
~ simplifies the assembly and manufacture procedure.
'~ In preferred e~bodiments, the tubular portion of
~;~ the housing is cylindrical, and ~he end portions are
circular. The two housing pieces can be composed o~ male
and female parts, or they could be composed of identical
parts. Each of the slots is defined by portions on both
'?~1 of the housing pieces. The end portions can have wall
~,i;, extensions that extend perpendicularly from the end
portions into the housing, partially define thP slots,
and strengthen the support of the terminals. The slots
can be perpendicular to or aligned with the seam formed
by joinder of the two housing pieces~ The terminals can
,~ have internal and external portions that are wider than
,¦ 20 middle portions that are situated within the slots,
~ thereby retaining the terminals in the ælots by
Jil interference with the housing. The fusible element can
be attached to the terminals by resistance welding or
~¦ ultrasonia welding. The fusihle element is preferably
corrugated, and multiple fusihle elements can be used.
~I The voids in the housing are preferably occupied by arc-
quenching fill material introduced into the housing via
fill holes that are sealed with preformed metal plugs or
nonconductive potting plugs after filling. The fill can
be a solid fill.
,` In another aspect, the invention features, in
general, a fuse in which terminals are retained in
, ~ respective slots through end portions of a tubular
', insulative housing by respective pins that each pass
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through a hole in the terminal and holes on both sides o~
the terminal in the end portions of the housing.
In a preferred embodiment, the housing is madz of
'i a tubular member with two ends and two slotted end blocks
~' 5 located at each of the two ends of the tubular member.
Each pin extends through holes at the ends of the tubular
~;~, member and holes in the end blocks.
Other advantages and features of the
invention will be apparent from the following description
of the particular embodiments thereof and from the
claims.
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Pescription of Particular Embodiments
Particular embodiments of the invention will now
be described~
Drawinqs
Fig. 1 is an exploded perspective view of a fuse
according to the invention.
Fig. lA is an enlarged view o~ the portion marked
; lA on Fig. 1.
,~ 20 Fig. 2 is a sectional view, taken at 2-2 of Fig.
1, of the Fig. 1 fuse.
Fig. 3 is a plan view, partially in section, o~
components of the Fig. 1 fuse during assembly.
Fig. 4 is an exploded perspective view o~ an
`; 25 alternative embodiment of a fuse according to the
~l invention.
j~ Fig. 5 is an exploded perspective view of another
;l alternative embodiment of a ~use according to the
ll invention.
'~ 30 Fig. 6 is a partial sectional view showing the
~ junction of housing pieces of the Fig. 1 fuse.
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Fig. 7 is an exploded perspective view of a fu~e
casing of an alternative embodiment of a fuse according
to the invention.
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Fig. 8 is a sectional vi~w, taken at 8-8 of FigO
7, of the Fig. 7 fus0 casing shown with a portion o~ a
terminal.
Fig. 9 is a plan view of a housing piece of the
~' Fig. 7 fuse casing.
Fig. 10 is a partial sectional view showing the
junction of housing pieces of the Fig. 7 fuse.
Structure, Manufacture, and Operation
Referring to Figs. 1, lA, 2 and 3, fuse 10
includes insulative housing pieces 12, 14 made of
plastic, terminals ~6 made of conducting material,
~usible elements 18 made of conducting mat~rial, and
plugs 19. Insulative housiny pieces 12, 14 have tubular
portions 20 and end portions 22. End portions 22 have
~l surfaces defining slots 24 and fill holes 26 after pieces
12, 14 have been joined together. Slots 24 extend
between and are defined by wall extensions 28, which
~s, extend into the interior of the housing. The long axis
'!','j'''l of each slot 24 (in the face of each end portion 22) i~
~1~ perpendicular to the seam formed when the two housing
pieces 12, 14 are joined. Terminals 16 include external
i 25 portions 30, internal portions 32, and middle portions 34
(within slots 24). External portions 30 have holes 60.
;l Fusible elements 18 are attached to opposite surfaces 36
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of internal portions 32. Fusible elements 18 have
l.ll current limiting notch sections 33 defined by rows of
1 30 holes and are generally corrugated to provide a
,~1 relatively larger number of notch sections 33 for a given
~, l length of housing than would be permitted if fusible
elemen~s 18 were straight.
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As shown in Fig. 2, the external portion 30 and
;l internal portion 32 of each terminal 16 are larger than
j the slots 24, and the middle portion 34 is essentially
the same size as the slot. This ensures that, a~ter
housing pieces 12, 14 have bePn joined, each terminal 16
is retained and anchored in the housing by interference
between its internal portion 32 and the walls defining
."! slot 24. Wall extensions 28 (Fig. 3) make the slots
deeper and thereby increase the support of terminals 16.
In manufactur2, the ends of fusible elements 18
are attached to surfaces 36 by resistance (spot or
continuous) welding or ultrasonic welding. The
subassembly of terminals 16 and attached fusible elements
18 is then inserted in housing piece 14. Housing piece
12 is placed in position, and pieces 12, 14 are joined to
each other.
When housing pieces 12, 14 are made of
thermoplastic material, they can be joined together by
,j ultrasonic welding. As shown in Fig. 1, housing pieces
12, 14 are identical and include mating edge surfaces 82.
When housing pieces 12, 14 are joined, projections 84 on
one piece coincide with ~lat portions of edge surface 82
~ on the other piece. Alternatively, all projections 84
;l could be on one piece, and all flat portions could be on
the other. Triangular projections 84 direct the
ultrasonic welding energy and increase the efficiency of
the welding process. When using ultrasonic welding to
~ ~oin housing pieces, it is preferred that the fusible
;,, !;',1 elements be aligned with the direction of vibration (as
in Fig. 1) and not perpendicular to it (as in the Fig. 4
¦ embodiment discussed below~.
Fig. 6 shows a different joint configuration, a
shear joint, which can be used along an edge and is
particularly preferred for semi crystalline material in
~, 35 order to obtain good joint strength. Upper piece 100 has
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right angle portion 102 including lower surface 104,
~, vertical surface 106, and upper surface 108. The mating
portion of lower piece llo has similar right angle
".`,.~f, portion including low~r surface 112, vertical surface
,,l 5 114, and upper surface 116. The other sides of pieces
100, 110 have the same mating configurations; piece 100
could have the projection defined by surfaces 104, 106 on
the inside (as it is shown on Fig. 6 for the right-hand
i side), in which case it would be considered a male piece
while piece 110 would be considered a female piece, or
~; the projection defined by surfaces 104, 106 could be on
the outside, in which case both pieces would be
identical. The overall wall thickness is about 0O13
~¦ thick, and there is between 0.012" and 0.016"
interference for the vertical surfaces used to permi~
~¦ ultrasonic welding. During such welding, lower piece
110 is fixed, and upper piece 100 is moved toward it and
vibrated at 20 KHz. The material of the interfering
~l vertical surfaces melts due to friction as the two are
brought together, resulting in a shear ~oint that has
! good bond strength. Energy directing triangular
~, pro;ections would still be used ak the ends of the tubes,
;;i, owing to geometry limitations.
f,'~, ~he thermoplastic material has the capability to
! 25 b~ melted and reformed while retaining its properties
when cooled below its melt point; this is desirable to
~; permit joinder of preformed housing pieces by welding and
, to avoid the use of adhesives. The material should also
have a sufficiently high continuous use temperature so as
, ~ 30 to maintain structural integrity at elevated temperatures
resulting from heating when operating at rated current
conditions. Preferably the continuous use temperature
(UL746C, 100,000 hour test) is greater than 110 C (most
~;!,', ~ preferably greater than 120 C). Fillers are preferably
added to the thermoplastic resins to reduce the cost of
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the material and to improve the mechanical properties of
the plastic by forming a support matrix within the
plastic. Fillers tend to increase the continuous use
temperature of the thermoplastic material, thereby
~'i 5 providing improved structural integrity at elevated
temperatures. However, depending on the resin and filler
'~l material, increasing filler concentration beyond a
certain amount tends to reduce the strength; also,
increasing the concentration beyond a certain amount may
tend to negatively affect the ability to create strong
bonds using ultrasonic welding. It accordingly is
desirable to increase the continuous use temperature as
much as possible while still achieving good bond strength
,i using ultrasonic welding. Suitable filler materials
include fiber glass, calcium carbonate, carbon fiber,
~ cellulose, and graphite fiber. In general, thermoplastic
;~ materials with a continuous use temperature above 110 C
and a filler concentration between 20% and 40% (most
¦ preferably between 30% and 35%) provide necessary
strength at elevated temperature while still permitting
processing by ultrasonic welding. The thermoplastic
l material also preferably includes a flame retardant, is
¦ nontoxic (not give off toxins when it melts), and has
,l high dielectric strength (above 400 volts/mil).
A suitable material for the thermoplastic material
~;1 is glass reinforced polyphthalamide semicrystalline resin
containing 33% glass filler available under the Amodel
i AF-1133 V0 trade designation from Amoco Performance
Products, Inc., Atlanta, GA. This material includes a
flame retardant and presently has a provisional rating by
Underwriters Laboratories Inc. for a continuous use
~/~; temperature of 115 C for electrical (the relevant
i~ continuous use temperature for the invention) and 130 C
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~i Other suitable materials include a highly
crystalline Nylon 4.6/ having 30% glass filler, and
available from DSM Corp. under the Stanyl trade
designation; polyphenylene sulfide having 30% glass
filler and availabla from Phillips Corp. under the Ryton
trade designation; and glass-filled liquid crystal
polymers such as Xydar from Amoco, Supec from General
Electric, and Vectra from Hoechst Celanese.
Also, some aspect of the inventions can be used
with thermoset materials that ara joined together by
~i adhesive or solvent bonding.
The use of identical housing pieces 12, 14 reduces
~l, the part count and simplifies the manufacturing
fi~','.l, procedure. The subassembly of terminals 16 and fusible
, 15 element 18 is advantageously easily installed at the same
~¦ time that the housing is formed from two pieces, and the
,!,,~1 terminals are anchored without crimping, staking,
;¦ welding, pinning or other techni~ues, owing to the fact
that terminal slots 24 are defined by facing housing
pieces 12, 14 and are smaller than interior portions 32.
Another technique for joining housing pieces 12,
¦ 14 toyether is by adhesive bonding, e.g., when the
I~i material is a thermoset plastic or also when it ls a
thermoplastic.
~;~ 25 After bonding pieces 12, 14 together, the void
pace resulting in the housing is filled with a granular
arc-quenching fill material (e.g., 50/70 or 40/60 quartz;
not shown) through fill holes 26 located in the end
portions of the housing. When the fuse employs a solid
fill, as with sodium silicate, fill already introduced
¦ into the housing is soaked with a liquid bath of the
sodium silicate, which wicks through the sand and is then
cured. Solid fill is preferably employed for
thermoplastic material6 to provide added strength to the
fuse at elevated temperatures.
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i~ Referring to Fig. 4, fuse 40 includes insulative
`,1 housing pieces 42, 44 made of plastic, terminals 46 made
of conducting material, pins 48 made of conducting
, material, fusible elements 18 made o~ conducting
material, and plugs 49. Insulative housing pieces 42, 44
have tubular portions 50 and end portions 52. A tubul~r
portion 50 has a hole 54 therethrough for receiving a
~;1 blown-fuse indicator (not shown). End portions 52
include pin holes 56 and recesses that define slots 58
after pieces 50 have been joined together. The long axis
of each slot 58 (in the ~are of end portion 52) is
~, parallel to the seam formed when the two housing pieces
42, 44 are joined. Terminals 46 include external
portions 62, internal portions 62, and middle portions 64
;~ 15 (within elots 58). Middle portions 64 include pin holes
66. Fusible elements 18 are attached to opposike
surfaces 68 of internal portions 62. End portions 52
~1 also have fill holes 53 therethrough for receiving fill
I material; holes 53 are sealed with preformed metal plugs
49 or a nonconductive potting plug.
Housing pieces 42, 44 are joined via mating
¦ grooves and projections. Housing pieces 42, 44 are
';j identical, each having a first side edge 86 with a
l projection 88 and a second side edge 90 with a groove 92
arranged so that the projection ~8 of the housing piece
42 ~its into the groove 92 of housing piece 44 and the
l projection on housing piece 44 fits into the groove on
housing piece 42. Alternatively, a groove 92 could be
provided on both sides of one housing piece (which would
then be considered the female piece) and a projection 88
could be provided on both sides o~ the other housing
~;I piece (which would then be conæidered the male piece).
Housing pieces 42, 44 can be bonded together by
ultrasonic welding, i~ made of thermoplastic material, or
'~ 35 by adhesive bonding.
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Terminals 46 are retained in the housing by pins
48 passing through pin holes 56 in the housing and pin
holes 66 in the terminals. These pins also can be used
to make an electrical connection to an indicator or
se~sor at the surface of the housing.
The housing is filled with an arc-quenching fill
(not shown) through fill holes 54 located in the tubular
~, portions of the housing. The fill can be granular or
-~ solid, as already described. Fill holes 54 are then
v5-l 10 sealed with plugs 49.
Referring to Fig. 5, fuse 70 includes tubular
`l housing 72 made of insulative material (e.g., a
'J.''"l thermoset), end blocks 74 made of either conducting or
insulative material, terminals 76 made of conducting
l 15 material, pins 48 made of conducting material, fusible
'~; elements 18 made of conducting material, and plug 75.
~ubular housing 72 has pin holes 78 (near the ends) and
~;l fill hole 96. Each end block 74 has a respective
terminal slot 77 and a single pin hole 80 that extends
~; 20 radially through the end block, perpendicular to the long
~¦ axis of slot 77.
erminals 76 and end blocks 74 are retained in
~¦ tubular housing 72 by pin~ 48 passing through pin holes
78, 80 in end blocks 74, and pin holes 98 in terminals
76.
¦ The housing is filled with an arc-~uenching fill
¦ (not shown) through fill hole 96 located in tubular
housing 72. The fill can be granular or solid, as
¦ already described. Fill hole 96 is then sealed with plug
75.
In the embodiment shown in Fig. 5 t tubular housing
72 can alternatively be made of glass melamine glass.
~j~ End blocks 74 can be made of plastic.
Re~erring to Figs. 7 - 10, fuse casing 120 is used
with terminals similar to those shown in Fig. 1. Instead
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of using wall extensions 28 to define slots 24 and
~i, support the terminals (as in the Fig. 1 embodiment), ~use
!'.',~'' casing 120 employs inner walls 122, which are spaced ~rom
associated end walls 124. Also, housing pieces 126, 128
of ~use casing 120 are joined by a shear joint at the
seam alony tubular walls 130 and end walls 124~ as shown
in detail in Fig. 10.
Housing pieces 126 and 128 are injection molded
from glass reinforced polyphthalamide semicrystalline
resin containinq 33% glass filler available under the
Amodel AF-1133 V0 trade designation from Amoco
Performance Products, Inc., Atlanta, GA. Inner walls 122
,'~,."! of housing pieces 126 and 128 do not extend fully across
the tubular region in the housing, but instead extend
from the tubular walls 130 about two-thirds of the way
toward the plane at the seam hetween pieces 126, 128.
.
fusible element (not shown in Fig. 7) is contained within
;.. ! cavity space 132 between inner walls 122. Transverse
~ ribs 13~ connect inner walls 122 to respective end walls
,,,,j~ 20 124. End walls 124 have slots 136 for receiving
terminals (e.g~, terminal 140 shown in Fig. 8), and inner
~ walls 122 have recessed surfaces 138 and side surfaces
,!; 139 aligned with slots 136 to define passages for
receiving the fuse terminals. ~s shown in Fig. 8,
terminal 140 has enlarged inner portion 142 tha~ is
~i larger across than the distance between opposed surfaces
138 of pieces 126 and 128, causing terminal 140 to be
~',5i retained therein. Terminal 140 i~ supported by the
siurface of end wall 124 defining slot 136 and ~urfaces
~! 30 138, 139 o~ inner walls 122; the distance between inner
wall 122 and end wall 124 provides stability. End wall
124 and tubular wall 130 are 0.091'l thick; inner walls
~ 122 are 0.060" thick. This arrangement provides good
s~ support for the terminals and avoids distortion problems
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that can occur when molded plastic pieces have large
regions of plastic.
Referring to Fig. 10, pieces 126 and 128 are
joined to each other at a shear joint formed between
mating seam portions 144 and 146 having stepped
configurations. The same shear joint construction is
employed at the tubular walls and both end walls. Seam
`~l portion 144 on housing piece 126 has lower surface 148
s~ (0.050" wide), vertical surface 150 (0.091" high), and
upper surface 152 (0.054" wide). Mating seam portion 146
~ of lower piece 128 has lower surface 154 ~0.040" wide),
,r~ major vertical surface 156 (0.071" high), interfering
shelf surface 158 (0.014ll wide), further short vertical
surface 160 (0.020" high) and upper surface 162 (U.050"
wide). Piece 126 is considered a male piece, while piece
128 is considered a female piece. The overall wall
thickness is about 0.091" thick, except at the seam,
where the wall is about 0.104" thick. There is a 0.004"
; clearance between short vertical surface 160 of piece 128
and vertical surface 150 of piece 126~ There is 0.010'
interference between ma~or vertical surface ~56 of
housing piece 128 and vertical surface 150 of housing
piece 126. During ultrasonic welding, lower piece 128 is
fixed, and upper piece 126 is moved toward it and
vibrated at 20 KHz. The material of the interfering
vertical surfaces melts due to friction as the two are
brought together, resulting in a shear joint that has
good bond strength.
~! Other embodiments of the invention are within the
scope of the following claims. E.g., a particular fuse
can include one or a plurality of fusible elements 18.
Also, the terminals of the Fig. 5 embodiment could be
insert molded in the end blocks. Also, o~her welding
techniques can be employed; e.g., the mating faces might
be heated by a source of heat (as opposed to friction)
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:~: and then joined together. Also, solvent bonding could be
:l used to join together two housing pieces. In addition to
~:j cylindrical fuse housings, other cylindrical shapes ~uch
, as those having square or hexagon cross sections can be
~, 5 used.
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